In direct injection systems the fuel is injected from a fuel pressure accumulator through injection valves into the combustion chambers of the internal combustion engine. In order to optimize the control of the injection process, the fuel temperature of the injected fuel, i.e. the temperature of the fuel in the injection valve, must be known as accurately as possible. Toward that end reference is generally made to the temperature of the fuel in the fuel pressure accumulator as an approximation.
The physical characteristics of the fuel, such as for example the density, the viscosity, the elasticity, the sound propagation velocity in the fuel, etc., are dependent on the temperature of the fuel. The physical characteristics of the fuel determine how the entire injection process proceeds, as well as the embodiment of the entire injection system. Knowledge of the fuel temperature is therefore used to adjust the parameters relevant to the injection process in order to achieve optimal injection and combustion.